PBX load testing with Twilio's cloud voice platform

One of our clients is a government agency that has very large call volumes surrounding certain events. These events are make-or-break things for the official that heads this agency, and past few have had some issues. Right when traffic would peak, their phone system would crash.

They hired us to provide management services and one of the initial projects was to investigate and solve this problem. Since all we had were stories of hysteria and crisis, with very little in the way of analysis, our first step was to stage a load test. Since that wasn't something their carrier could assist with, we decided to handle it ourselves.

It turns out this project was a perfect fit for Twilio's cloud voice platform. We've been a long-time Twilio customer for international SMS notifications (they're the guys that send SMS notifications to our portal users), so we have experience developing to their API and already have a web-based infrastructure set up to interact with their platform.

Our really bad load tester interfaceWe ended up developing a very simple web interface through which we could trigger a set number of calls to be pushed to a specific phone number. Our system would then have Twilio initiate calls, play a message informing the recipient that it was a load test and asking them not to hang up, and put the call into a queue with some terrible hold music.

Our load tester was able to load up their phone system, manipulate call traffic to simulate actual traffic, and test call behavior. In the process, we identified and resolved issues with their carrier's trunk overflow configuration as well as with their PBX, both of which would result in strange error messages to callers. In the end we collected a lot of data and were able to document our findings in such a way as to satisfy their requirement for due diligence. It's all about the CYA factor in politics, after all!

For this project, we had to maintain 180 total calls to saturate their two phone systems. Without access to an elastic cloud platform, we would have needed significant trunk and equipment resources to be able to do something like this. Instead, we were able to use capacity for a few hours at a fraction of the buying and using our own. Pretty sweet.

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